1. Field of the Invention
The present invention relates to multiplexing communication networks on vehicles and more particularly relates to providing a network having a central control module and one or more remote generic modules to provide control of non-standard vehicle vocations as well as specialized controllers for conventional vehicle vocations.
2. Description of the Prior Art
At a simple level, communication between two agents may be kept physically separated from communications occurring among other agents. Where two or more signals do not use the same physical space, there is no need to separate the signals in time or in carrier wave frequency. Such a communications regime is sometimes termed physical division multiplexing although the term multiplexing is usually reserved to techniques for applying multiple signals to a single medium or physical space. So called physical division multiplexing describes how motor vehicles have been traditionally wired. The use of separate dedicated wires to connect each switch and lamp is a type of physical division multiplexing. Obviously, physical division multiplexing, while simple in concept, results in the use of many wires (the classical motor vehicle electrical harness), which are difficult to install during manufacturing and problematic to maintain in the field.
Arrangements allowing a number of agents to communicate over a common physical layer or medium offer much greater physical simplicity. Intelligible communication between two or more devices among a greater plurality of devices, all over a common medium, depends upon the communicating devices being able to distinguish, and understand, messages directed to them from other messages which they receive, but which are not intended for them. The process of distinguishing messages depends upon the transmitter of the message applying some attribute to the message which identifies it to the intended recipient. In human conversation, most people readily distinguish speech directed to them from interfering crosstalk in a crowd by the distinctive aspects of the voice of the person addressing them. Where the members of the group are electrical components, the problem still involves identification of a distinguishing attribute of the signal. Appropriate attributes for signals take a number of forms.
A line communicating a signal from a remote switch to a lamp to turn on or off (by having a second switch, local to the lamp, change states to control connection of the lamp between a power bus and ground) cycles only rarely. In a typical trip such a change in state occurs only once or twice, if at all. Where such a line is not intended to provide power to the lamp, and simply indicates changes in state for the local switch controlling the lamp, the line will have the capacity to handle far more data than the occasional indications to turn a lamp on and off. The objective of maintaining simplicity in manufacturing and maintenance are preferably met by allowing communication among a number of components to occur in a single medium, or at least as few communication lines as possible. The line used to connect switch and lamp could interconnect a number of components, carrying messages between any grouping of elements connected to the line when not required to carry an instruction to a lamp to turn on. One way of achieving this objective is a communications regime which divides time into slots during which particular combinations of components have use of a signaling line. Such methods are well known in the art and are examples of time division multiplexing (TDM). In motor vehicles, time division and related multiplexing techniques offer substantial simplification in physical layer required to support the control of vehicle vocations.
Rigid time division multiplexed communications appear to interleave data signals into a single serial signal over a single physical medium. Multiplexed communication systems also provide the reverse function (demultiplexing) of dividing the single signal into multiple, nonsynchronous digital signals. Where demands on the capacity of the data transmission medium are not especially heavy, any unit may be allowed to claim the medium provided collision detection is provided for and other indicia, such as address headers, indicate the signal's destination.
As applied to motor vehicles, multiplexed communications over serial data paths are an effective technique for reducing the number of dedicated communication paths between the numerous switches, sensors, devices and gauges installed on the vehicles. With each increase in the number and variety of accessories and functions installed on each vehicle, the benefits of using a single, multiplexed communication serial link for passing instructions to and receiving information from vehicle devices as diverse as running lights and rear axle temperature sensors becomes greater. Multiplexing the signals to and from local controllers and switches for vehicle systems promises greater physical simplicity through displacing much of the vehicle wiring harness, reducing manufacturing costs, facilitating vehicle electrical load management, and enhancing system reliability.
The specific manner of implementing multiplexed communications is outside the scope of the present invention, which applies a defined protocol, the SAE J1939 protocol. The development by the Society of Automotive Engineers of the J1939 series of standards for multiplexed communications testifies to the progress in the application of multiplexed communications to vehicles. Standards have been or are being developed relating the communication path, transmission collision detection, diagnostic ports and data protocols, among other topics. The J1939 protocol provides an open protocol and definition of the performance requirements of the medium of the physical layer, but also allows for development of proprietary protocols. The SAE J1939 protocol is a specialized application of a manufacturing costs, and anticipated improvements in reliability. Notwithstanding this recognition, the teaching of the Windle patent falls short of teaching a generalized physical layer in which numerous specialized functions are implemented by programming. Windle et al. did not attempt to extend the idea of single design controller outside of an environment where the requirements on the controller could be fully anticipated nor did they attempt to remove specialized programming from the distributed controllers.
Numerous advantages would flow from enabling a manufacturer to provide a chassis with a generalized electrical control layer on which programming could add extensive functionality. For example, builders of luxury coaches, fire trucks and ambulances, all place highly specialized requirements on a vehicle's electrical system which may, or may not, be known to the chassis manufacturer. In some cases these requirements may even be unique to a particular vehicle. For example, a coach builder may wish to install a highly customized, zone activated air refrigeration system on a vehicle. Such specialized systems or vehicle vocations have required complex, customized wiring systems to support. Were a coach builder able to adapt a serial communication system to the functionality requirements of the various bodies, and further able to specify accessory functionality without the need to hardwire that functionality into the vehicle, substantial gains in physical simplicity and reliability could be achieved.
Substantial economies of scale could be gained from using a standardized component for several vocations on commercial vehicles. The ability to support such a device would also simplify assembly and allow for smaller parts inventories, as partially achieved by Windle et al. Such a generic control regime would allow greater differentiation in vehicles to be economically obtainable.
Windle et al. contemplated the use of fully reprogramable local controllers, which were adaptable to a defined sets of tasks by reprogramming. More recently, suppliers of major power train components have included a dedicated controller suitable for managing the component and for communicating with a vehicle electrical system controller using the open protocol of the J1939 standard. These suppliers allow a limited type of configuration programming of the controllers for changing the values of certain vehicle operating parameters. Configuration data has been used to change values of certain controlled parameters, such as engine horsepower/torque output curves, fuel rates and cruise control performance; however, the functional definition of the input and output interfaces of controllers have not been changed and the configuration programming continues to reside in the local controller.